The present invention relates to an electrophotographic copying machine having a document feeder, and more specifically to a document feeder with sorting capability regardless of the copying mode, be it single or duplex copying mode.
In an electrophotographic copying machine, a document placed on a document rest is optically scanned to form a corresponding electrostatic latent image on a uniformly charged photoreceptor as a recording medium. The latent image on the photoreceptor is visualized with toner at a developing section where the visualized image (toner image) is transferred by transfer means onto a copy paper which has been supplied in a timely manner. The copy paper onto which the image is transferred is separated from the photoreceptor and transported to a fixing device.
The fixing device is generally composed of thermal fixing rollers because of advantages in temperature control and compactness. The thermal fixing rollers serve to thermally fix the toner image on the copy paper. The fixing device may be composed of pressure fixing rollers which fix the toner image on the copy paper under pressure instead of heat. The copy paper on which the image is fixed is discharged out of the copying machine and sorted in accordance with the copying order on a copy tray.
Conventionally, a document to be copied is placed manually at a predetermined position on the document rest. Accordingly, each document must be replaced manually with a new one each time a copying operation is completed, which is quite troublesome. To avoid such a troublesome manual operation, an automatic document feeder is installed in the copying machine so that each document sheet is supplied and set at a predetermined position on the document rest by a transporting device provided on the document rest. With the copying machine equipped with the automatic document feeder, it is not necessary to manually replace an old document with a new one. Simultaneously, copying time is substantially saved. When copying documents with such a copying machine, a plurality of document sheets to be copied are piled on a document tray, normally with the image-bearing side downward, that is, faced towards the document tray. The document is supplied one by one either from the top or bottom of the document pile to the predetermined position on the document rest and optically scanned. After the image scanning, the document is transported away from the document rest while the next document is supplied to the predetermined position on the document rest.
Meanwhile, the copy papers on which image has been transferred are sorted in accordance with the copying order on the copy tray. For multiple copies of a plurality of documents, however, it is required to manually re-sort and arrange the copy papers in the copying order. To avoid this manual sorting operation, it is necessary to equip the copying machine with a plurality of copy trays, so that the copy papers are sorted and arranged on each of the copy trays in the same order as the original document sheets. Specifically, in making five copies of each document, five copies of the first document are delivered one by one to each of the five copy trays, and five copies of the second document are also delivered one by one to each of the five copy trays. This operation is repeated to the final document. In this case, it is necessary to discharge each copy paper in such a manner that the image-bearing side of the copy paper is faced to the copy tray.
As indicated in the above, an automatic document feeder and sorter, if added to a copying machine, can effect extremely simplified copying operation, substantially reduce the copying time and save time that would be required for sorting after copying operation. In addition to the single side copying function as described above, duplex copying function may be provided in the copying machine to provide for paper conservation. In applying duplex copying function after an image is formed on one side of a copy paper, another image is formed on the other side of the copy paper. In order to transfer a toner image formed on the photoreceptor onto the other side of the copy paper, the copying machine must be equipped with means to reverse the transport direction of the single sidecopied paper within the copying machine.
It is desired that the copying machine, in the duplex copying mode as well, be able to automatically feed and sort documents properly. In the conventional copying machine, however, document feeding and sorting mechanisms are devised only for single side copying operation. For instance, suppose three documents are to be copied one by one on each paper and that the three copy papers are to be sorted on one tray. When the documents are fed from the top (the third document), the copy papers on which images have been transferred are discharged on the copy tray with the image-transferred sides facing upward. In the duplex copying mode, the image on the third document is copied on one side of a paper, the image on the second document on the other side of the paper, and the image on the first document on one side of another paper with the other side left blank. Generally, however, it is preferable that the first and the second documents are copied on both sides of a paper and the third document on either side of another paper.
When the documents are fed to be copied from the bottom, the copy papers are discharged on the copy tray with the image-transferred sides facing downward. In this case, the first and the second documents are copied on both sides of one paper in the duplex copying mode. When discharged onto the copy tray, however, the second document image-transferred side is faced downward. Consequently, if three documents are copied in the duplex copying mode, the copy papers discharged are not sorted in accordance with the copying order. Thus, the sorter cannot fulfill its expected function in the duplex copying mode.